Disk drives are an important data storage technology. Read-write heads are one of the crucial components of a disk drive, directly communicating with a disk surface containing the data storage medium. It is crucial that each read-write head function reliably, otherwise the disk drive using that read-write head will fail to function reliably. This invention is focused on the optimized control of each read-write head during write operations within the disk drive. Before disclosing the invention, some relevant prior art will be discussed.
FIG. 1A illustrates a typical prior art high capacity disk drive 10 including actuator 30 with voice coil 32, actuator axis 40, actuator arms 50–58 with head gimbal assembly 60 placed among the disks.
FIG. 1B illustrates a typical prior art high capacity disk drive 10 with actuator 20 including actuator 30 with voice coil 32, actuator axis 40, actuator arms 50–56 and head gimbal assemblies 60–66 with the disks removed.
FIG. 2A illustrates a head gimbal assembly 60 including head suspension assembly with head slider 100 containing the read-write head 200 of the prior art.
Since the 1980's, high capacity disk drives 10 have used voice coil actuators 20–66 to position their read-write heads over specific tracks. The heads 200 are mounted on head sliders 100, which float a small distance off the disk drive surface 12 when in operation. The flotation process is referred to as an air bearing. The air bearing is formed by the read-write heads 200, illustrated in FIG. 2A, and slider-head gimbal assembly 60, as illustrated in FIGS. 1A–2A. The flying height of the air bearing is very small, often about 100 Angstroms, or about 0.4 millionths of an inch.
Often there is one head per head slider for a given disk drive surface. There are usually multiple heads in a single disk drive, but for economic reasons, usually only one voice coil actuator.
Voice coil actuators are further composed of a fixed magnet actuator 20 interacting with a time varying electromagnetic field induced by voice coil 32 to provide a lever action via actuator axis 40. The lever action acts to move actuator arms 50–56, positioning head gimbal assemblies 60–66, and their associated head sliders 100 containing read-write heads 200, over specific tracks with speed and accuracy. Actuators 30 are often considered to include voice coil 32, actuator axis 40, actuator arms 50–56 and head gimbal assemblies 60–66. An actuator 30 may have as few as a single actuator arm 50. A single actuator arm 52 may connect with two head gimbal assemblies 62 and 64, each with at least one head slider.
FIG. 2B illustrates the relationship between the principal axis of an actuator arm 50 containing head gimbal assembly 60, which in turn contains head slider 100, as found in the prior art.
FIG. 2C illustrates a simplified schematic of a disk drive controller 1000 of the prior art, used to control an assembled disk drive 10.
Disk drive controller 1000 controls an analog read-write interface 220 communicating resistivity found in the spin valve within read-write head 200.
Analog read-write interface 220 frequently includes a channel interface 222 communicating with pre-amplifier 224. Channel interface 222 receives commands, from embedded disk controller 100, setting at least the read_bias and write_bias.
Various disk drive analog read-write interfaces 220 may employ either a read current bias or a read voltage bias. By way of example, the resistance of the read head is determined by measuring the voltage drop (V_rd) across the read differential signal pair (r+ and r−) based upon the read bias current setting read_bias, using Ohm's Law.
Today, a disk drive performs an initialization process 1400 including what is often known as read channel optimization. Read channel optimization is supposed to find the best parameters for read/write operations, which include, at least, a read bias current (Ir), write current Iw and write boost.
Channel Statistical Measurements (CSM) are a standard system used in assembled disk drives to estimate channel performance, by measuring amplitude. The testing of disk drives by CSM gives only a partial quality measure. A more thorough quality measure is to determine the Bit Error Rate (BER).
As magnetic recording head 200 becomes smaller in physical size, there is an increased need optimize write field control in an assembled disk drive to minimize reliability problems. This need is difficult to fulfill, because it requires first discovering what are the reliability problem mechanisms within the assembled disk drive, and then configuring the disk drive to minimize the effects of the reliability problem mechanisms.